Upper Limit of Normal for Blood Eosinophils in Blood Count
The upper limit of normal for blood eosinophils in a complete blood count is 0.45 × 10^9/L (450 cells/μL). 1
Normal Range and Clinical Significance
- Blood eosinophilia is defined as elevation of eosinophils in the bloodstream above 450-550 cells/μL 2
- For clinical purposes, eosinophilia is typically categorized as:
- Mild: 450-1,500 cells/μL
- Moderate to severe (hypereosinophilia): >1,500 cells/μL 3
- Hypereosinophilia (HE) is formally defined as >1.5 × 10^9/L eosinophils in the blood on two examinations at least one month apart 1
Factors Affecting Blood Eosinophil Counts
- Blood eosinophil counts can vary significantly due to several factors:
- Seasonal variations with differences of approximately 20% between summer and winter months 4
- Comorbidities such as nasal polyps can increase eosinophil levels by up to 38% 4
- Current smoking can decrease eosinophil levels by approximately 23% 4
- Time from collection to analysis can reduce eosinophil counts and increase variability 4
Clinical Applications and Interpretation
- Blood eosinophil counts are used as biomarkers in several conditions:
- In respiratory diseases, counts ≥300 cells/μL can predict exacerbation risk with sensitivity of 0.71 and specificity of 0.64 5
- In eosinophilic esophagitis (EoE), peripheral eosinophilia occurs in 10-50% of adults and 20-100% of children, though usually only modestly elevated (2-fold) 1
- Blood eosinophil levels above 0.24 × 10^9/L (240 cells/μL) can predict high tissue eosinophilia with sensitivity 70.9% and specificity 78.4% 1
Stability and Measurement Considerations
- Eosinophil levels between 150-299 cells/μL show the least stability over time, with only 44% of patients remaining in this classification for 7 of 10 measurements 4
- Higher stability is observed for counts <150 cells/μL (59% stability) and ≥300 cells/μL (66% stability) 4
- A single measurement may not be sufficient when using eosinophil counts for diagnosis or management of eosinophilic conditions 4
Clinical Relevance in Specific Conditions
- In returning travelers and migrants from tropical regions, eosinophilia (>0.45 × 10^9/L) is common (8-10%) and often associated with helminth infections 1
- In asthma, the upper limit of normal for sputum eosinophil differential count is 1.9%, which differs from blood eosinophil normal ranges 1
- When evaluating for hypereosinophilic syndrome, counts persistently >1,500 cells/μL require further investigation for potential end-organ damage 3, 6
Understanding the normal range and variability of blood eosinophil counts is essential for proper clinical interpretation, especially when using these values to guide treatment decisions or monitor disease activity.